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Showing 2 results for Magmatic Evolution
Petrography, Geochemistry, Magmatic Evolution and Tectenomagmatic setting of Igneous Rocks Associated with Nikuyeh Epithermal Mineralization (west of Qazvin)
Soheila Aghajani, Dr Majid Ghasemi Siani, Dr Mohammad Hashem Emami, Dr Mohammad Lotfi, Dr Kazem Gholizadeh,
Volume 6, Issue 1 (8-2020)
Abstract
The Nikuyeh district is located south of the Tarom-Hashtjin metallogenic province in Western Alborz. Oligo-Miocene subvolcanic intrusion and Mid-Eocene volcanic rocks with composition of dacite (hybrid dacite) to andesite are main igneous units associated with Nikuyeh polymetallic epithermal ore mineralization. Subvolcanic igneous phase consists of I type porphyritic monzodiorite to quartz monzonite and quartz syenite (quartz syenite), and have an average alkali (Na2O+K2O) content of 4.62- 9.9 wt%, and K2O/Na2O content of 0.45- 1.66. The chemical compositions of igneous rocks show that belong to meta- alumina series, high–K calc-alkaline to shoshonitic rocks. Sieve-textured and zoning in plagioclase, corrosion and rounded of phenocrysts, presence of quartz xenocrysts, zoning and bimodal composition of clinopyroxene phenocrysts and presence of hybrid dacite and its three different glass compositions show physicochemical disequilibrium and probably magmatic mixing. Spider diagrams show that igneous rocks are enriched in in large ion lithophile elements (LILE) and depleted in Ta, Nb and Ti which these features are typical of the subduction-related magmas. On the other hand, highly LILE/HFSE and LREE/HREE ratios, low content of TiO2 (<1 percent), and high Ba/Ta ratio are subduction magma features. Tectonic setting diagrams show that district volcanic rocks have high–K calc-alkaline, and subvolcanic rocks located in volcanic arc granitoid (VAG).
 
Geochemistry of apatite in various felsic rocks of the Piranshahr plutonic complex: an approach to investigate magmatic evolution
Dr Seyed Ali Mazhari, Dr Kwan-Nang Pang,
Volume 9, Issue 2 (12-2023)
Abstract
The felsic intrusive rocks in the Piranshahr plutonic complex consist of three groups: syenite, nepheline-syenite, and alkali-feldspar granite. They are co-genetic and formed approximately 40 million years ago. Textural relationships, major oxides, and trace element composition of the selected felsic rock samples were studied using SEM, EPMA, and LA-ICP-MS methods. In the studied samples, apatite appears as euhedral to subhedral crystals with prismatic forms and has a homogeneous texture without zonation. The low amounts of MnO and the REE pattern of apatites confirm their magmatic nature, indicating that post-crystallization processes did not affect the composition of apatites. All apatite crystals fall into the fluorapatite category. The amounts of fluorine and chlorine vary in different felsic rocks, and the F/Cl ratio decreases from granites towards syenites and nepheline-syenites. The determination of the apatite saturation temperature indicates that alkali feldspar granites have a higher crystallization temperature range (858-844°C) than both syenites (818-783°C) and nepheline syenites (668-610°C). Analyzing the manganese levels in the examined apatites suggests a consistent oxidizing setting with minimal fluctuations in fO2 conditions (logfO2= -8 to -9.8). Trace elements in different apatites show significant differences; for instance, apatites in granitic samples are enriched with HFSE and rare earth elements (REE), while apatites in nepheline-syenites have a higher concentration of components such as silica, Cr, Ni, and V. The composition of trace elements and the F/Cl ratios in apatites demonstrate consistent variations and alignment with the host rock composition. The results of the apatite mineral composition confirm previous petrological findings regarding the impact of volatile phases separation on magmatic evolution in the Piranshahr felsic rocks.

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